lighten
darken
There aren't any precise antonyms but "dull" is probably the closest.
darken
The likely word is "darken" (where to bleach means to whiten).
The opposite of "illuminate" is "darken," which means to make something less bright or to obscure it. While "illuminate" implies bringing light or clarity to a subject, "darken" suggests the removal of light or the introduction of confusion. Another related term could be "obscure," which emphasizes making something unclear or difficult to understand.
Amber is actually a dark orange. Red and Yellow make orange so darken the orange with its opposite in this case blue.
Actually it is best to try and avoid using black to darken a color. A lot depends on the medium being used. In paints a good way to darken a color is to mix it with a small bit of it's opposite. For example: to darken blue add a small bit of orange. Try to reserve black for those times you absolutely need it. A 'rich black' can also be created by mixing the three primary colors.
To make colors darker, you can add black to the original color. This process is called shading. Alternatively, you can mix the color with its complementary color (opposite on the color wheel) to darken it.
Some glaucoma medicines will darken the iris color.
The noun forms for the verb to darken are darkener and the gerund, darkening.
You can darken your hair using the Black Ice spray, or the natural remedies such as herbs sage and rosemary.
And She Would Darken the Memory was created on 2007-07-16.